I've seen there are "gold" flash diffusers like the ones from sto-fen that are supposed to give, surprise, warmer "sunset-like" light. Since I couldn't find any decent reviews...

... does anyone use this kind of diffuser, when does it make sense (broad range of situations or only as a very special effect)? Any sense buying this over flash gels except that gels are a hassle to mount to the flash in addition to a diffuser?

Its supposed to match your flash to tungsten light, its geared to make a daylight source closer to 3200, but i find the canon 580exII is warmer than daylight and it doesnt quite match 3200 on that flash. Its more like 4000-4400 (depending on how warm you like your image) to get reasonably accurate white balance from the flash. It can give a nice effect when trying match ambiant light.

If you want to "warm" an image up. Tungsten light like others have mentioned. I prefer gels, bit more accurate with 1/4, 1/2 and full cuts so you can pick and choose (CTO that is for warming). If you don't mind abusing your gels a little bit you can jam them under a standard Sto Fen diffuser and BOOM you have a gelled diffuser~